THURSDAY, Dec. 7, 2017 (HealthDay News) -- Women with earlier-stage breast cancer may be able to spend less time on hormonal therapy without dimming their prognosis, a new study suggests.

In a trial of nearly 3,500 patients, researchers found that seven years of hormonal therapy was as effective as 10 years. By the study's end, more than three-quarters of women in both groups were alive and recurrence-free.

The results are "important," according to experts attending the San Antonio Breast Cancer Symposium, where the study was released Thursday.

"Potentially, there is a large group of patients who don't need 10 years of therapy," said Dr. Susan Domchek, of the University of Pennsylvania's Abramson Cancer Center.

Domchek, who was not involved in the study, said decisions around hormonal therapy are often a source of "major discussion and angst" for patients and doctors.

Hormonal therapy involves drugs that block estrogen from fueling the growth of breast cancer cells. They include tamoxifen and a group of medications called aromatase inhibitors, such as anastrozole (Arimidex).

The problem is, the drugs can have difficult side effects like bone fractures, hot flashes, sexual dysfunction and muscle and joint pain.

Some women do well on the medications, Domchek noted, while others "feel terrible and want to come off them."

So, treatment decisions are always individual, she said, based on various factors, including a woman's personal likelihood of having a breast cancer recurrence.

Dr. Erica Mayer, another cancer specialist who was not involved in the study, made the same point.

The new findings "will ultimately offer us more choices to help tailor therapy for individual patients," said Mayer, a senior physician at Dana-Farber Cancer Institute in Boston.

She also stressed the bigger picture. "An important take-away here is that women with this disease are doing better than ever before," Mayer said. "Most patients in this study were still alive and doing well."

For years, it's been standard for women with early breast cancer to go on hormonal therapy for five years. The hope is to prevent the cancer from coming back.

More recently, studies have found that extending hormonal therapy beyond five years can further cut the risk of recurrence.

But it hasn't been clear how long women should stick with that extra treatment, said Dr. Michael Gnant, the lead researcher on the new study.

To help answer the question, his team recruited nearly 3,500 women with early stage breast cancer who underwent surgery and other standard treatments. That included five years of hormonal therapy with tamoxifen, an aromatase inhibitor or both.

The researchers randomly assigned the women to either two or five additional years of hormonal therapy -- which meant either seven or 10 years total.

In the end, the study found, the benefits in both groups were the same: An average of 14 years after their diagnosis, 78 percent of women in both groups were alive and free of a cancer recurrence.

Plus, shorter treatment meant a lower risk of bone fractures: 4 percent of women on seven years of therapy suffered a bone break, versus 6 percent of those in the 10-year group.

The implications are clear, according to Gnant, of the Medical University of Vienna's Comprehensive Cancer Center in Austria.

"Two additional years is sufficient," he said. "There is no reason to escalate adjuvant [hormonal] therapy beyond seven years total. This can help reduce side effects, including fractures."

However, Domchek and Mayer stopped short of saying that.

It's still possible, they said, that certain women at high risk of a recurrence could benefit from longer treatment.

For example, Domchek said, the risk of a long-term recurrence varies according to whether the initial breast cancer had invaded nearby lymph nodes. That means women with 10 affected lymph nodes have a higher risk than those with no affected lymph nodes.

Mayer agreed. "I don't think this study tells us that we need to do one thing versus the other," she said.

Instead, she said, it offers important information for doctors and patients to use in making a "personalized" treatment plan.

The study was funded by the drug company AstraZeneca, which makes several hormonal therapies for breast cancer.

Research presented at meetings is usually considered preliminary until peer-reviewed for publication in a medical journal.